Wind Power Generation - Renewable Energy: Technology, Economics and Environment - page 331

prevent reciprocal shut-down of the converters and to ensure relatively undis-
turbed wind conditions for every converter. Shadowing refers to the subsumed
effects of closely arranged wind energy converters that take away the wind from
each other and to the enhanced dynamic strain placed on downwind installed wind
energy converters due to the increased turbulence within the downwind flow of
the converters placed in front.
On principle, with regard to minimised shadowing there are two different ar-
rangements of wind energy converters within a wind park of limited space. Be-
sides optimised converter arrangement towards a preferred wind direction there is
also the possibility of an optimised converter installation without a preferred air-
flow direction (Fig. 7.22), maintaining a certain distance between the individual
converters to even out the imbalance between the reduced airflow speed due to
energy extraction by the rotor and the undisturbed airflow. For the following con-
verter almost undisturbed wind conditions may be assumed. The required distance
between the individual converters depends on meteorological, topographical and
other site-specific conditions (such as legal or administrative restrictions) and may
vary widely.
The minimum distance between two converters standing next to each other is
referred to by the distance factor k A which is defined as the ratio of converter dis-
tance to rotor diameter. The required distance between the individual converters is
thus a multiple of the rotor diameter.

Ideal wind mill arrangement without
preferred wind direction

Ideal wind mill arrangement with
preferred wind direction

Main wind direction

(x)

(y)

Wind mill
location
Necessary distance area

Fig. 7.22 Alternatives of wind converter arrangements within a wind park (schematic rep-
resentation; see /7-1/)

If a determined site has a preferred wind direction, and provided that its topog-
raphic conditions are favourable to the installation of wind energy converters (e.g.
plains near the coast), converters may be arranged in several rows behind each
other (Fig. 7.22, right). Since under the described conditions wind mainly blows
from one direction, shadowing effects only need to be minimised for the main